Green colour of the visible spectrum is ineffective in inducing flowering whereas blue colour induces poor flowering. The wavelength 580 nm to 680 nm in the red portion of the spectrum has been found to be most effective for inducing flowering.
Flowering is a phytochrome mediated process. It occurs in 2 possible forms. The form which absorbs red light (660 nm) is PR and the form which absorbs far red light is termed PFR. PR stimulates flowering while PFR inhibits it. The two forms are easily interconvertible.
The red light and far red light exposures showed that in flowering also the last exposure determines the response.